The field of this invention is that of semiconductor circuit systems and the invention relates more particularly to a composite metal material for use in mounting semiconductor devices in such systems.
Related subject matter is disclosed in a commonly assigned copending patent application filed of even date herewith entitled A COMPOSITE MATERIAL AND METHOD FOR MAKING, Ser. No. 07/166,300 filed Mar. 10, 1988.
Conventional electronic systems employ a variety of circuit board substrates and the like for mounting semiconductor devices such as integrated circuit chips and the like. In such systems, it is known to be desirable to provide substrate materials which have coefficients of thermal expansion corresponding to those of the semiconductor devices to be mounted thereon, whereby the semiconductor devices can remain securely mounted and electrically connected to circuits on the substrates during thermal cycling of the systems. It is also known to be desirable to provide substrate materials with substantial thermal conductivity properties for dissipating heat from the semiconductor devices during operation of the devices, thereby to improve operating and reliability characteristics of the devices and systems. It is also known to employ composite metal materials in such substrates to combine relatively low coefficient of thermal expansion characteristics of one metal material with relatively high thermal conductivity characteristics of another metal material, thereby to provide composite materials having desirable combinations of coefficient of expansion and thermal conductivity properties.
For example, U.S. Pat. No. 3,399,332 provides a grid of a metal material of relatively low coefficient of thermal expansion having openings in the grid filled with a copper material or the like of relatively higher thermal conductivity to provide a mounting for a semiconductor device having a desired combination of thermal expansion and conductivity properties. In another embodiment, the patent suggests that particles of a ferrous alloy can be impregnated into a copper material for providing an alternate material having selected thermal expansion and conductivity properties. U.S. Pat. No. 4,283,464 provides two grids of a metal material of relatively low coefficient of thermal expansion on either side of an inner layer of copper metal for providing a composite substrate material having another described combination of thermal expansion and conductivity properties. U.S. Pat. No. 4,472,672 shows layer combinations of ferrous metal materials of relatively low thermal expansion properties with layer materials of relatively high thermal conductivity where the layer thicknesses are regulated to be within selected ranges for providing composite metal materials with coefficients of thermal expansion substantially corresponding to those of semiconductor devices to be mounted thereon. U.S. Pat. Nos. 3,097,329 and 4,158,719 show composite metal materials formed by powder metallurgy techniques or the like either by compacting mixtures of metal powders of relatively low coefficient of thermal expansion with metal powders of relatively high thermal conductivity materials and then heating the compacted powders for diffusion bonding the particles to each other or by compacting and sintering one of the metal powders to form a porous sintered compact and by then filling the pores of that sintered compact with a melt of the other metal material.
However each of such previously known composite metal substrate materials has been subject to some objection. Thus the composite metal materials shown in U.S. Pat. Nos. 3,399,332 and 4,283,464 are difficult to manufacture and to apply to specific circuit system applications; the composite metal material shown in U.S. Pat. No. 4,472,762 does not provide desirably high thermal conductivity in all directions; and the composite metal materials shown in U.S. Pat. Nos. 3,097,329 and 4,158,719 are not found to provide desirable combinations of thermal expansion and conductivity properties because of the manner in which they are made.